Method of making road surfaces



Patented Sept. 15, 1931 PATENT OFFICE SAM EVERETT FINLEY, 0F ATLANTA, GEORGIA METHOD OF MAKING ROAD SURFACES No Drawing.

The invention relates to a novel and superior method of forming the finishing surface of pavements during their construction, and of refinishing or renewing the surfaces of pavements of previous construction.

The object of the invention is the production of a bitumen-bound surface having the general characteristics of a low-void hotmix pavement, such as sheet asphalt or a fine graded asphaltic concrete, through the coating, in place of comparatively finegraded mineral aggregates, either alone or in combination with coarser aggregates, with a bituminous binder, while both are cold and in their natural state, the coating being attained by a novel application of the principles of surface tension. A new and more stable result secures a thoroughly homogeneous mixture which is so workable as to permit of spreading in a ver thin layer, if so desired, and which rapid y matures into a stable, wear-resistant, and close grained surface having the desired percentage of voids.

The invention provides a novel, economical and superior method of securing, for the so-called lower types of pavement, a surface equal to that of the highest types of pavement; and in like manner, a novel and superior method of re-surfacing old pavements in such a manner as to correct the de-.

fects resulting from wear, age, or the action of the elements, or from the deficiencies of original construction.

In sheet asphalt, asphaltic concrete, and the various standard pavements of a similar character, the finishing surface is by preference as close grained as possible, and containing the lowest possible percentage of voids. In these high-type pavements the aggregates and the bitumens are premixed before application, usually with the assistance of artificial heat. Their successful application therefore requires the existence of an expensive and cumbersome heating and mixing plant, or necessitates a freight haul from such plant, entailing considerable expcnse. The application of these plant-mixed materials is generally made under the in- Application filed November 11, 1929. Serial 110. 406,535.

fluence of artificial heat, but, whether heated or unheated, pre-mixed materials are very difficult of application to a road surface in a thin layer, for the following reasons. If the materials are applied hot, as is generally the case, they tend to cool quickly when spread out in a thin layer, making proper distribution and compaction exceedingly diflicult. If the materials are pre-mixed and then transported and laid while cold, it is necessary that they retain workability through the period of their application, and this end is achieved in the prior art by the use of a light bitumen, the use of a bitumen in combination with a liquefier or the use of a minimum quantity of the bitumen used, in order to produce a dry and cold mixture.

lVith any or all of these precautions practiced, it has still been difficult to secure a mixture that Was workable, even in a comparatively thick layer. The present inven tion eliminates the foregoing disadvantages and provides a novel and superior method of coating aggregates whose combination provides a mixture with a predetermined percentage of voids with bituminous cement, when both are in place upon the roadway, and when both are cold, and in their natural state. It provides a resultant mixture of the two Which is entirely homogeneous, and which is workable to a greater degree than has heretofore been possible, therefore al- -lowing application in a thinner layer than heretofore possible; and it allows a bitumen content sufficient to achieve the superior results hereinafter described.

In surface treatment and in bituminous macadam, by the nature of their construction, it has been impossible under the prior art to secure a uniform, close-grained, and water-proofed surface, since the materials heretofore used in such surfaces, through necessity, have been of a relatively large size, in order that they might be coated, or at least partially coated, by the cementing medium, by those methods used in the prior art. In bituminous macadam construction the aggregates secure their coating through the flowing and penetrating of the heated and liquefied bituminous cement as it is poured or sprayed over the aggregates, lying in place, cold, and in their raw state. It is essential that these aggregates be coarse and open, and containing a large percentage of voids, in order to facilitate the movement of the bitumens.

It has been the practice to use aggregates of a comparatively uniform size, and a minimum size of three-fourths inch, for the main structures of such roadways, requir- -in on the average a minimum content of voids of thirty per cent. For the finishing surface, materials ranging in size from three-fourths inch to one-fourth inch, and containing about the same minimum content of voids have been generally used. Recognizing the value of a surface containing a low voidage the art has striven to pulverize these surface aggregates after application, through continual rollin or other means. Experience has shown, l iowever, that it is practically impossible to secure the required coating of the particles without a high content of voids.

Furthermore, under the prior methods employed for the construction of a bituminous macadam finishing surface, it has been impossible to secure an entire coating, or a uniform coating, of the bituminous material over the surface of the articles. In fact, the average percentage 0 the surfaces coated, as related to the whole, has been generally conceived to not exceed sixty per cent. This uncoated area represents a very distinct inferiority in this type of surface, even when using the aggregates. sized as in past practice. The present invention, in contradistinction, so treats and prepares the sur faces of these particles that a one hundred per cent and thoroughly uniform coating is assured, thus vastly improving this type of construction, even when practiced with those sizes of aggregates used in the old art. In surface treatments the same general difliculties have been encountered. The thickness of such treatments, and the sizes of the aggregates used in the old art are generally similar to the sizes and quantities used as a surface for bituminous macadam as outlined above and the same difficulties have been encountered in securin a thorough coating of the aggregates an in limit- ,ing the sizes of the aggregates. The higher character of thoroughly waterroofed and stable wearing surface with a ow voidage has been barred to bituminous macadam and surface treated roadways.

Furthermore, the prior art has never deemed it necessary or sound practice for a low-voidage finishin surface to be of an considerable depth. n the contrary, suc art has pointed to an attempt to make such surface as thin as practical. The minimum conceived as practical has been generally the minimum point of workability, as up to the present time no successful method has been devised for properly applying a very thin surface course, and at the same time securing the uniform distribution, compaction, and stability necessary, without materially increasing the cost.

he repairing and resurfacing of old pavements having defects in their structure or surface, but whose general strength is sufficient to carry the traffic load, is an engineering problem solved in a novel and superior manner by this invention. The ap plication ofa thin, wear-resistant, high-type surface, for such pavements is combined under this method with a thorough repair of any cracks or defects that may exist in the old pavement. Worn surfaces are readily replaced, open surfaces are closed and Waterproofed, cracked surfaces are permanently healed and repaired, and a smooth, beautiful, and stable surface is applied to any old pavement at a slight cost.

The method of this invention permits of a thorough and eflicient coating of all the aggregates containing either a low, high or medium content of voids with the cementing medium. It provides a mixture of aggregates and bitumens which readily adapts itself to movement and proper distribution, without materially increasing the cost. It permits the distribution of bitumens, when cold, throughout the aggregates, when cold, in such a manner as to secure a new and superior result through the gradation of percentages from top to bottom of the mass as hereinafter more fully explained. It is the first successful method of mixing such combination of mineral aggregates as will result in a mass of comparatively low voidage with bituminous cements in place upon the roadway. It makes possible, as a finish course for any type of pavement, a thinner high-type surface, and therefore a less expensive one, than has been possible up to the present time.

I am able to obtain these highly novel, meritorious, and revolutionary results through a novel application of the princi les of surface tension, hereinafter more fu lly described, which permits the use for such surfaces of aggregates more dense, finer, or with a lower percentage of voids than has been hithereto possible, and at the same time assures a complete and uniform coating of the same with the bituminous materials. This permits for the first time a surfacing for this type of construction which is e ual, if not superior, to the plantmixed sur aces.

An outstanding feature 'of this invention results in the fact that I utilize the said novel ap lication of surface tension to effect filling of the voids between the aggregates from the bottom upwardly. Heretofore the III aggregates have been either mixed with the b tuminousmaterial before laying, or such" aggregates have been first distributed in a layer and the bituminous material poured" or sprayed over them, so as to flow or work downwardl by gravity through the aggro gates to the voids. In accordance with the resent invention, in contradistinction, the Bituminous material is first spread in predetermined quantities and the a gregates are then spread over the vitumlnous material. My novel application of surface tension is thereupon rendered effective to cause the bituminous material torise between the aggregates until it fills the voids to the very wearing surface of the mass, which is meanwhile agitated and rolledto the desired surface contour. Such a proceeding is in marked contradistinction to all prior practice.

I will now describe different practical embodiments of the invention, but the examples given are to ,be understood as illustrative only, and not as defining the limits of the invention as regards percentages, proportions and particular materials employed.

In the practice of m invention I first thoroughly clean the sur ace of the roadway. This surface may be the surface of any suitable road base, or the surface of a part or section to be refinished. In some instances it may be desirable to prime the ex osed surface with a light bitumen, in or or to.

facilitate a cementitious bond.

Having previously determined the desired thickness of the resultant wearing surface,

I now apply to the surface of the old road-' way a uniform coating of a stable bituminous cement suiiicient in quantity to provide the desired percentage of cementing medium for the character and quantity of materials to be used as a mineral aggregate. Such amount I determine in the following manner.

If I desire to secure a surface one-half inch in thickness, and approximating sheet asphalt in its characteristics, I secure sand or rock detritus whose screen analysis would make it acceptable for sheet asphalt work. The following standard screen analysis for sheet asphalt would be appropriate, although not exclusive.

Passing 10 mesh 98% to 100% Passing 10 mesh and retained on 40 14% to 50% Passing 40 mesh and retained on 80 30% to 60% Passing 80 mesh and retained on 200 16% to 40% Passing 260 mesh 0% t0 5% Such a sand would carry a definite percentage of bitumen, easily determined with-V in close limits by engineering practice, dependent upon the exact analysis. The an'munt. of bitumen needed when the semi was in combination with a mineral filler r id be between nine and eleven per cent of ihe whole. Without the mineral. filler, percentage needed re-ski be tween seven and nine. The use of this percentage of bitumen in' combination with this aggregate, when plant mixed according to past I practice, would produce a proper result for sheet asphalt construction. Such a sheet asphalt mixture, however, has the same percentage of bitumen content throughout its entire mass. It has of necessity to be a some what dry. mixture, to permit of workability and to'prevent subsequent shoving and waving. This invention, therefore, makes possible a more satisfactor result, as it. ispossible to provide'a hig er bitumen content in the bottom portion of the wearing sur-v richer mixture at the point of contact with I the lower structure, thus insuring a continued cementitious bond between-the two. It provides a reservoir of bitumens from which the surface itself may serve itself up to its maximum content. And it providesa continued mixture of the entire structure sutfi ciently rich in bitumens to be elastic and rubbery, and plastic to the point of selfhealing in case of injury. I therefore pref' erably use a percentage of bitumen slightly in excess" of that percentage that would be used in sheet-as halt. In the example cited, one-half inch oi the materials named in the case of a sheet mixture would wei h about fifty pounds [per square yard. avithout filler, the average bitumen content needed for the sheet mix above would be approximately four pounds,'or one-half gallon, per square yard.v I would therefore apply approximately five-eighths gallon to the surface of the roadway.

In like manner, if I desire to secure a surface three-eighths inch in thickness? and approximately a fine graded as'phalticconcrete in'its characteristics, I secure a mineral aggregate whose screen analysis would make it acceptable for such work. Its size may be in general within the following limits:

Passing and retained on 10 mesh 20% .to 35% Pas i. and retained on 40 mesh 8% to 30% Pas s0 and retained 0h 80 mesh 12% to 40% Pas SO and retained on 200 mesh 10% to 25% Passing 200 mesh 0 to 6% The percentage of bitumen carried by such as. 1 *gregate is readily determined. It be in general from 6% to 8%. If

mesh mineral filler was added, the fie would carry between 7% and 9% of *7"- .nnen. Tbs-c may be determined as a matter of engineering practice in hot mix construction. For the reasons quoted above I would increase the percentage of bitumen somewhat over that ordinarily used in plant mixtures, and would therefore preferably use an amount slightly in excess of the two and one-half pounds per square yard that would be required under the average of the above for three-eighths of an inch, and would apply approximately three pounds, or threeeighths of a gallon per yard.

In like manner I determine the amount of this application for each particular circumstance and aggregate and depth of surface I desire to produce.

Having previously determined the mineral aggregate to be used, as outlined above, I prepare this aggregate by coating it with a light petroleum hydrocarbon in an amount sufficient to entirely coat the surfaces of the particles, and moisten the mass. The per centage needed, as related to the quantity of aggregate is generally approximately 10.

Any suitable light hydrocarbon may be used without departing from this invention, but I preferably employ a blend of quick and slow diffusion hydrocarbons. Hydrocarbon distillates from crude oil, boiling below 280 F. have been found to give thoroughly satisfactory results. For example, I have found that an admixture or blend of approximately per cent naphtha of quick diffusion and 30 per cent of slow diffusion, produces highly satisfactory results.

I preferably prepare theaggregate by coating the particles before their application to the surface of the roadway, but such preparation may be accomplished by first applying the raw aggregates to the surface and then applying the light hydrocarbon to their surfaces by spraying the proper amount over them;

Immediately after this preparation, and before volatilization of the liquid, I spread the prepared aggregate over the surface of the application of bituminous cement, in such quantity per square yard as has been previously determined. I then lightly screed, broom, or move the aggregate about, either by hand or by mechanical device, in order to assist it in maturing. I continue this movement, or brooming until the surface indicates that the bitumen has been drawn up and absorbed by the aggregate to the point where it begins to set up. I then work or spread the material to a true cross-section and grade, and roll or compactit.

In order to assist the maturing of the surface during the process of rolling and compacting, I preferably moisten the rolls with the light hydrocarbon used in preparing the aggregate, or apply a very light spray f this material in advance of-the roller. This may also be used as a method of correcting possible deficiencies of original application, or as a means of making workable the surface aggregates in instances when weather or other delays have made impracticable their distribution or compaction at that period of their maturing when they are properly workable. 4

In following the above method of procedure, I have found that I obtain an entire- 1y novel and ve superior result through the application 0 the principles of surface tension. The hydrocarbon liquefier in the aggregate, movingfirst downward upon the bitumen by gravity, and then upward through the aggregate by volatilization, materially assists the natural capillarity and movement of the bitumen creating a strong surface tension over the surfaces of the particles of the aggregate, and by first liquefying by contact and then drawing by diffusion the bitumens over the prepared surfaces of the particles.

I have found that by the time volatilizetion has progressed to the point that the mass begins to stiffen, a thoroughly homogeneous mixture of the aggregate and the bitumens has been achieved, in an entirely new way, and that a careful spreading and compaction of the mass, followed by continued volatilization, produces a finished surface of great stability and resistance to wear, equal, if not superior, to the plant mixes.

The application of a thin high-type low void surface under this method is possible at a much lower cost than under the prior art, and makes available an economical method of repairing and re-surfacing old concrete roads or cracked and disintegrated asphaltic surfaces, by the addition of a thin, self-healing, plastic, and wear-resistant surface that is entirely water-proof, will not shove or wave, and presents a. pleasing appearance. This invention makes available a low cost result that is equal to or superior to high cost results. i

In the carrying out of the present invention, the bitumens employed may be either a coal tar product or an asphalt product, such as are common-as binding media in road construction. These bitumens are commonly called stable road-binders. The asphalts generally range in consistency between a. penetration of about 40 to a pene- Cal purpose, but those having boiling temperatures below 280 F. volatilize more rapidly and so mature sooner and are therefore preferably employed. I wish it understood, however, that I do not restrict this invention to any particular wetting or solvent agent as any suitable agent which will perform. the function stated in the manner described may be used in lieu of the particular hydrocarbon blend to which I have referred.

The present invention is applicable for use either as a surfacing for existing roads or as a finishing coat for roads of new construction. It has been found in practice to give very satisfactory results in connection with road repair and is useful in this con nection on pavements of all kinds including brick, Portland cement concrete, and the like, as well as penetration macadam or bituminous macadam roads.

The foregoing description sets forth the invention in its preferred practical form, but the invention is to be understood as fully commensurate with the appended claims.

Having thus fully described the invention, what I claim as new and desire to secure by Letters Patent is:

1. The method of making road surfaces, which consists in applying to the road base to be surfaced a coating of cementing matcrial in sufficient quantities to substantially fill the voids of the a gregates to be used in the surface strata o the road, and thereafter depositing upon said coating a layer of mineral aggregates with a volatile liquefier in sufficient quantity to wet the surfaces of the aggregate articles and provide an excess of the liquefier to work down and act upon the cementing material.

2. The method of making road surfaces, which consists in applying to the road base to be surfaced a coating of bituminous material in sufficient quantities to substantially fill the voids of the aggregates to be used in the surface strata of the road, and thereafter depositing upon said coating a layer of mineral aggregates with a volatile liqueficr in sufficient quantity to wet the surfaces of the aggregate particles and provide an excess of the liquefier to work down and act upon the bituminous material.

The method of making road surfaces, which consists in applying to the road base to be surfaced a coating of bituminous ma.- terial in sufficient quantities to substantially fill the voids of the aggregates to be used in the surface strata of the road, and thereafter depositing upon said coating a layer.

of mineral aggregates with a volatile hydrocarbon in sufficient quantity to wet the surfaces of the aggregate particles and provide an cxccss of the hydrocarbon to work down and act upon the bituminous material.

4. The method of making road surfaces, which consists in applying to the road base to be surfaced a coating of bituminous mate rial in sufficient quantities to substantially fill the voids of the aggregates to be used in the surface strata of the road, and thereafter depositing upon said coating a layer of mineral aggregates with a hydrocarbon liquefier in sufficient quantity to wet the surfaces of the aggregate particles and provide an excess of the hydrocarbon to work down and act upon the bituminous material.

5. The method of making road surfaces, which consists in applying to the road base to be surfaced a coating of cementing material in sufficient quantities to substantially fill the voids of the aggregates to be used in the surface strata of the road, and thereafter depositing upon said coating a layer of mineral aggregates with a volatile liquefier in sufficient quantity to wet the surfaces of the aggregate particles and provide an excess of the liquefier to work down and act upon the cementing material, agitating the aggregates until the surface indicates that the bituminous material has been drawn up and absorbed by the aggregate mass, and thereupon compacting the mass with the desired surface contour.

6. The method of making road surfaces, which consists in applying to the road base to be surfaced a coating of cementing medium in sufficient quantities to substantially fill the voids of the aggregates to be used in the surface strata of the road, thereafter depositing upon said medium a layer of mineral aggregates with a volatile liquefier in sufficient quantities to thoroughly wet the aggregates and provide an excess to act upon the cementing medium, and permitting the liquefier to first move downwardly by gravity through the aggregates into contact with the cementing medium and then upward through the aggregates by volatilization for the purpose of assisting natural capillary action by an accompanying creation of surface tension over the surfaces of the aggregates to draw the cementing medium over the wet surfaces of the aggregates by diffusion, and thereafter compacting the mass with the desired contour.

7. The method of making road surfaces, which consists in applying to the road base to be surfaced a coatlng of bituminous material in sufficient quantities to substantially fill the voids of the aggregates to be used in the surface strata of the road, thereafter depositing upon said material a layer of mineral aggregates with a volatile liquefier in sufficient quantities to thoroughly wet the aggregates and provide an excess to act upon the bituminous material, and permitting the liquefier to first move downwardly by gravity through the aggregates into contact with the bituminous material and then upward through the aggregates by volatilization for the purpose of assisting natural capillary ac- 7 after depositing upon said material a layer of mineral aggregates with a hydrocarbon liquefier in suflicient quantities to thoroughly wet the aggregates and provide an excess to act upon the bituminous material, and permitting the liquefier to first move downwardly by gravity through the aggregates into contact with the bituminous material and then upward through the aggregates by volatilization for the purpose of assisting natural capillary action by an accompanying creation of surface tension over the surfaces of the aggregates to draw the bituminous material over the wet surfaces of the aggregates by diffusion and thereafter compacting the mass with the desired contour. 9. The method of making road surfaces, which consists in applying to the road base to be surfaced a coating of stable bituminous material in sufiicient quantities to substantially fill the voids of the aggregates to be used in the surface strata of the road, thereafter depositing upon the said coating a layer of mineral aggregates with a sufiicient amount of volatile liquefier to thoroughly wet the aggregates and provide an excess adapted to seep down through the aggregates and produce a solvent action upon said bituminous material, thereupon agitating the mass to bring the liquefier into intimate contact with the bituminous material and to expedite evaporation of the liquefier for the purpose of creating a strong surface tension over the surfaces of the aggregates and to draw, by diffusion, the bituminous material over the thus prepared surfaces of the aggregates, and thereupon compacting the mass with the desired surface contour. .10. The method of making road surfaces, which consists in applying to the road base to be surfaced a suitable primer, then depositing thereon a coating of stable bituminous material in sufiicient quantities to substantially fill the voids of the aggregates to be used in the surface strata of thereafter depositing upon the said coating a layer of mineral aggregates with a sufiicient amount of volatile liquefier to thoroughly wet the aggregates and provide an excess adapted to seep down through the aggregates and produce a solvent action upon said bituminous material, thereupon agitating the mass to bring the liquefier into the road,

intimate contact with the bitumino'us material and to expedite evaporation of the liquefier for the purpose of creating a strong surface tension over the surfaces of the aggregates and to draw, by diffusion, the bituminous material over the thus prepared surfaces of the aggregates, and thereupon compacting the mass with the desired surface contour.

11. The method of making road surfaces, which consists in applying to the road base to be surfaced a light bituminous primer, then spreading thereover a layer of stable bituminous cement, then spreading over said cement a quantity of mineral aggregates together with sufficient hydrocar on liquefier to thoroughly wet the aggregates and provide an excess to gravitate'into contact with the bituminous cement, then agitating the aggregate mass until the bituminous material has been drawn up to thoroughly permeate said mass, and then compacting the whole with the desired contour.

In testimony whereof I have signed the foregoing specification.

SAM EVERETT FINLEY. 

